Stochastic Simulation of Crash
Structures
Paul Wood
Materials Characterisation and Simulation Project
© 2006 IARC
Project Partners
OEM
SUPPLIERS
IARC
CONSULTING
IARC
SUPPLIERS
© 2006 IARC
Stochastic Simulation of Crash Structures
2
Crash Test Requirements
Australia
Safety Standards
Regulated by Law
Europe
NCAP
Japan
Crash Tests
USA
Ensure minimum
crash safety protection
to occupants inside
vehicle
Test Outcome:
Pass/Fail
More challenging crash
tests
ƒ car makers encouraged
to develop safer vehicles
ƒvehicle insurance rating
ƒsafety sells vehicles
Test Outcome:
Safety Score
© 2006 IARC
Stochastic Simulation of Crash Structures
3
NCAP Crash Test Procedures
A
B
C
D
© 2006 IARC
Stochastic Simulation of Crash Structures
4
NCAP Crash Test Drivers
Good
Adequate
Marginal
Weak
Poor
Test dummies for front and side
impact contain sensing equipment
to measure forces, accelerations
and displacements during crash
tests
The measurements relate to injury
criteria e.g. HIC, chest acceleration
and rib displacements. A scored is
assigned using a star rating which is
published for public viewing on NCAP
websites
© 2006 IARC
Stochastic Simulation of Crash Structures
5
Example of NCAP Crash Test Results
a. Example of Low NCAP
b. Example of High NCAP
Score (c.2003)
Score (c.2003)
Adult occupant rating
Pedestrian rating
Test Scores:
Front 4 (25%)
Side 14 (78%)
Pedestrian 4 (11%)
Adult occupant rating
Pedestrian rating
Test Scores:
Front 15 (94%)
Side 18 (100%)
Pedestrian 10 (28%)
© 2006 IARC
Stochastic Simulation of Crash Structures
6
Virtual Crash Testing
Acceleration (g)
Structure Acceleration versus Time During Impact
0
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Time (sec)
Protection:
Good
Adequate
Marginal
Weak
Poor
NCAP SCORE
© 2006 IARC
Stochastic Simulation of Crash Structures
7
Typical Engineering Tolerances
Typical structural property and noise factors variations;
Structural
Properties
Boundary
Conditions
Distribution
Model Applied
Description
Range
Materials
+/- 10%
Uniform?
Gauges
+/- 10%
Uniform?
Joints
+/- 20%
Skewed ?
Manufacturing effects
+/- 10%
Skewed ?
Barrier angle
+/- 1 deg
Normal
Impact velocity
+ 3%
Normal
© 2006 IARC
Stochastic Simulation of Crash Structures
8
Modelling Variability
Typical parent distribution models;
Normal Distribution
Skewed Distribution
Uniform Distribution
Bi-modal Distribution
© 2006 IARC
Stochastic Simulation of Crash Structures
9
USNCAP Performance Variability
Structure Acceleration versus Time During Impact
Acceleration (g)
NOMINAL
UPPER BOUND
LOWER BOUND
RANDOM VARIABLE DATA
0
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Time (sec)
© 2006 IARC
Stochastic Simulation of Crash Structures
10
Characterising Performance Variability
STRUCTURE ACCELERATION v. TIME PROFILES
ACCELERATION (g)
Histogram of Peak Acceleration
LEGEND
UPPER BOUND
LOWER BOUND
NOMINAL
0
0.00
0.35
Lower Bound
(struc prop)
0.01
0.02
Most Likely Response
0.03
0.04
0.05
0.06
0.07
0.08
TIME (sec)
Relative Frequency
0.3
Nominal
(struc prop)
Upper Bound
(struc prop)
0.25
0.2
0.15
0.1
0.05
0
48
Peak Acceleration
© 2006 IARC
Stochastic Simulation of Crash Structures
11
Performance Variability & Relationship to Target
Histogram of Peak Acceleration with Target
0.35
TARGET
Pass
Fail
Relative Frequency
0.3
Nominal
(struc prop)
0.25
0.2
0.15
0.1
0.05
0
49
Peak Acceleration
© 2006 IARC
Stochastic Simulation of Crash Structures
12
Sample Estimate of Performance Variability
Histogram Comparing Sample Estimate and Parent Population
0.4
Average (most likely)
TARGET
0.35
Relative Frequency
0.3
0.25
Nominal
0.2
Assumed
Parent
population
0.15
0.1
Sample
estimate
(13 runs)
0.05
0
47
Peak Acceleration
© 2006 IARC
Stochastic Simulation of Crash Structures
13
Univariate v. Bivariate
Bivariate - Maximum Acceleration v. Crash Displacement
Peak Acceleration
Nominal
Random
RandomVariable
VariableData
Data
Upper Bound
Lower Bound
45
650
Displacement
© 2006 IARC
Stochastic Simulation of Crash Structures
14
Investigate Suitability of Structural Design Metric
STRUCTURE ACCELERATION v. TIME PROFILES
LEGEND
UPPER BOUND
LOWER BOUND
NOMINAL
ACCELERATION (g)
Define random
variables in crash
structure
Submit to CAE
Output from CAE
Input to occupant
RESPONSE FROM DRIVER & PASSENGER
model
Output from
occupant model
0
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
TIME (sec)
LHS
RHS
HIC
MAXBOUND
MINBOUND
Improved
NCAP score
300
41
© 2006 IARC
CHEST ACCELERATION (g)
Stochastic Simulation of Crash Structures
15
Characterise Structural Performance
CHARACTERISING STRUCTURAL ACCELERATION BY TIME AVERAGES
Acceleration (g)
ORIGINAL DATA 0.3msec
TIME AVERAGE = 2msec
TIME AVERAGE = 5msec
TIME AVERAGE = 10msec
TIME AVERAGE = 20msec
0
0
Time (s)
© 2006 IARC
Stochastic Simulation of Crash Structures
16
Validate New Structural Design Metric
CORRELATION BETWEEN OCCUPANT INJURY AND STRUCTURAL
PERFORMANCE MEASURES
1.00
CORRELATION VALUE
0.80
0.60
0.40
0.20
0.00
-0.20
-0.40
-0.60
-0.80
AVE
0-65
LHD HIC 36.0
MAX MAX MAX MAX MAX MIN MIN MAX MAX MAX
AVE
AVE AVE AVE AVE
AVE MAX
AVE
0-25 30- 30- 50- 50- 20- 20- 30- 50- 5030(0
(30 65- (V=0
0-80 0-25
5-25
at
50 50 at 70 70 at 30 30 at 50
70 70 at
65
TO TO
80 TO
0.65 0.63 0.60 0.08 0.24 -0.07 0.64 0.87 0.15 -0.31 0.04 -0.34 0.37 0.19 -0.48 0.01 -0.34 0.37 0.19
LHD CHEST ACCEL (g) 0.82 0.82 0.82 -0.53 -0.39 -0.13 0.83 0.60 -0.01 -0.43 0.43 -0.08 0.32 -0.07 -0.15 -0.19 -0.08 0.32 -0.07
LHD P.COMBI(%)
0.87 0.87 0.86 -0.40 -0.26 -0.17 0.88 0.77 0.07 -0.42 0.30 -0.21 0.37 0.13 -0.28 -0.14 -0.21 0.37 0.13
STRUCTURE
INDICATORS
StructuralPERFORMANCE
Performance Measures
© 2006 IARC
Stochastic Simulation of Crash Structures
17
Check Sensitivity of New Structural Design Metric
CORRELATION BETWEEN INJURY AND NEW STRUCTURAL
PERFORMANCE MEASURE
y = mx + c
R = 0.83
CHEST G
R2 = 0.69
43
31
NEW STRUCTURAL DESIGN METRIC
© 2006 IARC
Stochastic Simulation of Crash Structures
18
Conventional Structural Design Metric
CHEST G
CORRELATION BETWEEN INJURY AND CONVENTIONAL STRUCTURAL
PERFORMANCE MEASURE
No relationship
43
6
CONVENTIONAL STRUCTURAL DESIGN METRIC
© 2006 IARC
Stochastic Simulation of Crash Structures
19
Correlation Between New Structural Design Metric
and Structural Properties
Statistical Correlation Between Injury Performance Measure and
Structural Crash Properties
CORRELATION COEFFIENT (R)
1.00
High correlation to
0.80
structural inputs
0.60
0.40
0.20
0.00
0
50
100
150
200
250
-0.20
-0.40
-0.60
-0.80
-1.00
STRUCTURAL PROPERY ID
© 2006 IARC
Stochastic Simulation of Crash Structures
20
Establish Transfer Function Between New Structural
Design Metric and Structural Properties
STRUCTURAL DESIGN METRIC
RELATIONSHIP BETWEEN STRUCTURAL DESIGN METRIC AND
STRUCTURAL PROPERTY
Y = M1X + C1
Y = M2x + C2
25
2000
CHASSIS RAIL PROPERTY
© 2006 IARC
Stochastic Simulation of Crash Structures
21
Establish Likely Performance Modes and
Dependencies
11.00
BIVARIATE PLOT OF OP's FOR WTOL WITH DIRECTIONAL INPUT DEPENDENCIES IDENTIFIED WITHIN
EACH PERFORMANCE MODE ACROSS MODE
ACROSS MODE
SUBSTRATE GAUGE 1 TO 3 m m
WITHIN MODE & ALONG LSQ LINE
DOG HOUSE GAUGE
RIBS B GAUGE
10.00
FAILURE CLIP TIME 2
LSQ LINE
MAXIMUM DISPLACEMENT
9.00
ACROSS MODE
SUBSTRATE GAUGE 1 TO 3 m m
WITHIN MODE & NORMAL TO LSQ LINE
8.00
FAILURE CLIP TIME 1
LSQ LINE
SUBSTRATE GAUGE 2 TO 6 m m
WITHIN MODE & NORMAL TO LSQ LINE
TRIM YIELD STRESS
LSQ LINE
SUBSTRATE GAUGE
FRICTION VEHICLE SINGLE SURFACE
FRICTION HEAD TO TRIM
FAILURE CLIP TIME 4
ACROSS MODE
SUBSTRATE GAUGE 2 TO 6 m m
WITHIN MODE & ALONG LSQ LINE
TRIM YIELD STRESS
SUBSTRATE GAUGE
DOGHOUSE GAUGE
FRICTION RIBS TO A POST CLOSER
FRICTION A POST TO SUBSTRATE CLOSER
ACROSS MODE
SUBSTRATE GAUGE 0.5 TO 1.5 m m
WITHIN MODE & ALONG LSQ LINE
7.00
FRICTION HEAD TO TRIM
6.00
ACROSS MODE
SUBSTRATE GAUGE 0.5 TO 1.5 m m
WITHIN MODE & NORMAL TO LSQ LINE
SUBSTRATE GAUGE
DOGHOUSE GAUGE
FAILURE CLIP TIME 2
5.00
4.00
200
400
600
800
1000
1200
STOL ELLIPSE (2xSIGMA)
CLUSTER_3_ELLIPSE WTOL (2xsigma)
CLUSTER_2_ELLIPSE WTOL (2xsigma)
CLUSTER_1_ELLIPSE WTOL (2xsigma)
1400
1600
1800
HIC
© 2006 IARC
Stochastic Simulation of Crash Structures
22